10.44am:Occupy London protesters have taken over an abandoned office block near Liverpool Street station in central London belonging to investment bank UBS in an escalation of their protests against the banking sector and the government's response to the financial crisis.

They say they are going to open a "bank of ideas" there tomorrow, with talks from Palestinian activists and comedy from Josie Long, as well as contributions from trader Alessio Rastani. "Offices and meeting rooms will be available for those that have lost their nurseries, community centres and youth clubs due to savage government spending cuts."

They say the protesters "gained access to the building and secured it" last night, "giving them a legal claim on the space".

One of the demonstrators is quoted drawing attention to the fact some properties stand empty while homes are repossessed. Jack Holburn said:

Whilst over 9,000 families were kicked out of their homes in the last three months for failing to keep up mortgage payments – mostly due to the recession caused by the banks – UBS and others financial giants are sitting on massive abandoned properties. As banks repossess families' homes, empty bank property needs to be repossessed by the public. Yesterday we learned that the government has failed to create public value out of banking failure. We can do better. We hope this is the first in a wave of 'public repossessions' of property belonging to the companies that crashed the global economy.

The statement says this is a "non-residential occupation" and tells protesters not to bring their sleeping bags.

10.57am: If you refresh the page, I've posted a picture taken by my colleague Peter Walker of two security guards outside the occupied UBS building.

UBS building occupied by Occupy London today. Photograph: Peter Walker for the Guardian Peter Walker/Guardian

11.03am: My colleague Peter Walker is down at the new occupation and has just been allowed into the new building. He writes:

The new building is a huge, four-storey office building of, I'd guess, 1970s vintage. It was occupied last night, and has a notice in the window saying it is being squatted. Those inside say there are just under 30 people in there. There are some private security guards around, and City police have also just turned up.

Those inside say that apart from the Occupy movement's other priorities and global finance and social justice they want to highlight govenment moves to criminalise squatting.

The website says artists, performers and "creatives" are welcome to come and "transform the space". Games, workshops and "skillshares on anything from yoga to yahtzee" are also encouraged. "The only prerequisite is that this space is not for financial transactions. Trade in ideas or skills, but no one should need to pay to take part in the Bank's activities."

View from roof of UBS building occupied by Occupy London protesters today. Photograph: Peter Walker for the Guardian Peter Walker/Guardian

11.21am: Peter Walker has taken this photo (above) of the view from the roof of the building. He says the building opposite is also empty and being occupied by the protesters. On Twitter he adds:

twitpic.com/7fqx07 Just one of the several hundred empty rooms #olsx say they have here

Oddly, this building connects onto the one used as base for G20 protesters in 2009, which police raided #olsx

11.27am: I have just been talking to a spokeswoman for UBS. She said: "At the moment all we can say is: we are aware, we know they're there, and we're taking appropriate action."

She said the company had been in touch with the police and was taking "legal action" over the occupation.

11.30am:Peter Walker sends more from the occupied UBS building.

I've just had a tour of some of the building which Occupy hope to turn into their "Bank of Ideas", where people can meet and exchange thoughts.

It's actually several buildings clustered round each other, all in various states of disuse and disrepair. Our guide, Pete Phoenix, an environmental consultant and squatting activist, estimated that there could be as many as 500 rooms in all. The entire complex is owned by banking giant UBS, whose own, more modern London HQ is across the road.

The building, Phoenix said, will have a range of purposes. Apart from hosting events, its vast size and emptiness serve as a symbol of waste and overuse. "This winter there's people freezing on the streets, and look at all of this wasted space," he said.

There are also plans to highlight the government's plans to criminalise all squatting, a clause in a wider crime bill currently in the Lords. Opponents say existing laws are perfectly good enough to evict problem squatters and all the new measure will do is criminalise vulnerable homeless people who use derelict buildings for shelter.

I'm writing this from the roof of one of the buildings, about four floors up. On the street below I can see a couple of TV crews but the police seem to have gone.

This is a privately-owned building, so while UBS will need to get a court order to evict Occupy, this will most likely happen sooner rather than later.

11.37am: I have just been talking to a spokesman for the Metropolitan police. He said that private security guards were dealing with the occupation; if UBS wanted the police's help they would have to call them. But the Met was "aware" of the situation, he said.

11.38am: The police are sending out somewhat mixed messages. I just spoke to a City of London police spokeswoman, who said the occupation was on the Metropolitan police's patch (see 11.37am). But Peter Walker has just sent me this:

A car load of City police have just turned up. For some reason the police are heavily armed - even a machine gun. No idea why they're here.

11.51am: Peter Walker has asked the police what they are up to. They say they had calls that there was trouble or disturbances at UBS's headquarters across the road – which there has not been, Peter says.

11.56am: Back at St Paul's, the protesters are waiting to hear what the Corporation of London's next move is after the Corporation gave them until 6pm yesterday to leave or face being taken to the high court. I just called a spokesman for the Corporation, who said the local authority was going to go to the high court at some point next week, but when exactly "depends on the backlog at the high court".

11.58am:Peter Walker sends more on the arrival of the police at the UBS building a little earlier.

We just had some brief drama here. More or less as soon as I was escorted out of the building so the occupiers could hold a meeting, several heavily armed police arrived – they had a machine guns as well as handguns – followed by a few more vans.

The police looked very jumpy, ready for action. Protesters started leaning from the windows, worried.

Overhearing a chat between an officer and two activists, it transpired that police had received calls about a supposed disturbance at the UBS building across the road. The protesters assured police this wasn't the case.

Things feel more calm now, but there's still plenty of police around, and a police helicopter hovering over the building.

Police outside occupied UBS building in London today. Photograph: Peter Walker for the Guardian Peter Walker/Guardian

12.10pm: Peter Walker says the police that arrived at the UBS building were from the Metropolitan police and the City of London police. They have all left now.

Can everyone stop using the word repossess please? I recognise that it's a neat twist on bank repossessions but inexact regarding #occupylsx

An Occupy London protester in the occupied UBS building in London today. Photograph: Peter Macdiarmid/Getty Images

12.40pm: There doesn't seem to have been very much coverage of this occupation among other media organisations; as far as I can tell BBC News and Sky News have both completely ignored it. But Getty have sent a photographer who has filed some good pictures, including this one.

12.42pm: Peter Walker reports that Occupy have just organised a press conference on the occupation of the UBS building.

12.48pm: Peter Walker writes: "We've just been allowed back into the building – well, one room, anyway – for a press conference. So far they're just reading out the press release. Q&A upcoming."

1.33pm: The Occupy protesters have just finished their press conference, reports Peter Walker. It was a slightly makeshift affair at which about a dozen activists sat on the floor – a slightly tatty blue office carpet – in a ground floor room, a giant Occupy London banner on the wall behind them.

After one activist read out their press release about the new occupation, there was a brief Q&A. What did we learn? Well, according to regular camp spokesman Ronan McNern, the building will be "a space for political discussion", hosting this weekend's conference of UK Occupy movements.

To prevent their squatters' rights being undermined, the space will not be open officially to the public, just "guests and friends". But as one activist, Peter Phoenix, said with a smile: "We do have a lot of friends." In other words, turn up and you'll be let in.

They say they want to avoid confrontation with police and have contacted the UBS subsidiary which owns the building to see if they can some to some sort of agreement over its use. Perhaps to little surprise they've heard nothing as yet.

And why UBS? Well, in the main I just think it's a good, useable space in a convenient location. The activists are repeating allegations aired in some UK papers a few years back that UBS's purchase of a package of controversial mortgages called secured appreciation mortgages, mainly sold to older homeowners in the UK in the late 90s, has made the bank a profit of near £1bn at the expense of said pensioners. Nothing illegal has ever been alleged in this, and it wasn't UBS who initially sold the mortgages.

McNern said: "UBS is representative of the sort of bank which is not acting in the public interest. This is a public repossession of their empty building."

3.02pm: Peter Walker is still down at the UBS building on Sun Street, where there is not very much happening: no police, a few photographers, a couple of Occupiers taking in the view from the roof.

Across the road in the UBS building all the blinds facing the occupation and its banners seemed to be pulled down. Perhaps on official orders, who knows.

I've tried to engage a few post-lunch passers-by in suits about their thoughts on the new action but without success. That's the inevitable problem with this, unlike a very open camp, like St Paul's, where everyone mixes. Whatever the necessary reasons, it seems to reinforce the divide between protesters and others. Let's hope they can invite a few bankers in for a chat next week.

3.08pm:Peter Walker also points out that the complex of inter-connected buildings owned by a subsidiary of Swiss banking giant UBS appear to have been empty for several years.

The new occupation has been assisted by members of squatters' rights groups, who hope to also use it to highlight an imminent new law which will make the practice a criminal offence, Peter says. Currently, so long as a building was empty and there was no criminal damage in gaining entry, squatters must be evicted via the civil courts.

At a press conference inside the building, Occupy activists said they hoped to avoid confrontation with police by negotiating with UBS to use the empty complex by agreement. Attempts to contact the bank had thus far been unanswered, they said.

The Guardian was given a tour of much of the main building, comprising dozens of empty office suites in generally good repair, although there was some damp and damaged plaster.

Aside from the building's size and location, near many other financial institutions, the activists say it was chosen as it is owned by a major bank, and one which was bailed out by taxpayers, albeit those in Switzerland. Ronan McNern, a regular camp spokesman, said: "UBS is representative of the sort of bank which is not acting in the public interest. This is a public repossession of their empty building."

• Occupy London demonstrators have opened up a new front in their campaign against the banking industry and the government's response to the financial crisis by taking over a complex of buildings owned by a subsidiary of UBS bank just north of the City of London.

• The Occupy protesters aim to use the building as a space for political discussion, calling it a "Bank of Ideas". They plan to welcome artists and performers, use the space as a replacement for closed-down nurseries, community centres and youth clubs, and highlight government moves to criminalise squatting. UBS and the police seem prepared to leave them there for now, although a UBS spokeswoman did say the bank was taking "legal action" against them (see 11.27am).

•The Corporation of London says it will take the Occupy protesters at St Paul's Cathderal to the high court at some point next week, although evicting them could still take months (see 11.56am). There is speculation the protesters could now move their base to the UBS building – a far warmer prospect than the steps of St Paul's as winter draws in – although so far the demonstrators have said only a minimum of activists will be sleeping there (see 11.03am).

•The move seems to illustrate the protesters' continuing mastery of media strategy – despite the superficially chaotic atmosphere at their St Paul's HQ. They have now put UBS in much the same position St Paul's was in, forcing the bank to choose between allowing them to stay or setting themselves up as a symbol of the kind of unacceptable capitalism the protesters oppose. The ball is now in their court.